Aqueous synthetic resin dispersions

ABSTRACT

An aqueous synthetic resin dispersion consisting of (A) from 35 to 60% by weight of a synthetic resin prepared by free radical solution polymerization of a monomer mixture A1 and monomer mixture A2, wherein mixture A1 is (a) from 1.5 to 15% by weight of at least one C 3-5  unsaturated monocarboxylic acid, maleic or itaconic acid or anhydride and half-esters of maleic acid or itaconic acid with a C 1-8  ankanol or with glycol monoethers, (b) from 65 to 98.5% by weight of at least one C 1-10  alkyl (meth)acrylate, and optionally at least one C 11-20  alkyl (meth)acrylate (III), vinyl aromatic monomer (IV), mercaptosilane (V), and copolymerizable monomer (VI), and mixture A2 is (a) from 60 to 100% by weight of at least one monomer II, and optionally at least one monomer III, IV or VI and compound (V), with the proviso that more than 65% by weight of the sum total of A1 and A2 is accounted for by monomers II and an amount of compound V which differs from ) and is incorporated in the copolymer; 
     (B) from 0.05 to 5% by weight of at least one epoxy group containing silane; and 
     (C) at least one of ammonia and an organic amine; with the remainder being water and wherein the dispersion contains from 0 to 5% organic solvent.

The present invention relates to aqueous synthetic resin dispersionsconsisting of

(A) from 35 to 60% by weight of a synthetic resin, obtainable by freeradical solution polymerization, carried out spatially separately and/orin succession but spatially at the same point, of from 15 to 70 parts byweight of a monomer mixture Al and from 30 to 85 parts by weight of amonomer mixture A2, composed of

A1: (a) from 1.5 to 15% by weight of one or more monomers comprisingα,β-monoethylenically unsaturated mono- and/or dicarboxylic acids of 3to 5 carbon atoms, anhydrides of these dicarboxylic acids or half-estersof these dicarboxylic acids with alkanols of 1 to 8 carbon atoms orglycol monoethers (monomers I),

(b) from 65 to 98.5% by weight of one or more acrylates and/ormethacrylates of C₁ -C₁₀ -alkanols (monomers II),

(c) from 0 to 10% by weight of one or more acrylates and/ormethacrylates of C₁₁ -C₂₀ -alkanols (monomers III),

(d) from 0 to 20% by weight of one or more vinylaromatic monomers(monomers IV),

(e) from 0 to 5% by weight of one or more mercaptosilanes of the generalformula I (monomers V) ##STR1## where n is from 1 to 8, R¹ and R² areeach hydrogen and/or C₁ -C₁₄ -alkyl and R³, R⁴ and R⁵ are each C₁ -C₆-alkyl and/or C₁ -C₆ alkoxy, with the proviso that one or more of theradicals R³ to R⁵ is alkoxy,

and

(f) from 0 to 10% by weight of one or more other copolymerizablemonomers (monomers VI),

and

A2: (a) from 60 to 100% by weight of one or more monomers II,

(b) from 0 to 10% by weight of one or more monomers III,

(c) from 0 to 30% by weight of one or more monomers IV and VI and

(d) from 0 to 5% by weight of one or more monomers V,

with the proviso that more than 65% by weight of the sum total of A1 andA2 is accounted for by monomers II whose homopolymers have a glasstransition temperature of from 0° to -70° C., and an amount of monomersV which differs from. 0,

(B) from 0.05 to 5% by weight, based on the synthetic resin A, of one ormore silanes of the general formula II ##STR2## where R⁶ is anepoxy-carrying radical, (C) effective amounts of ammonia and/or of anorganic amine

(D) from 0 to 5% by weight of a nonaqueous solvent,

(E) the remainder being water.

The present invention furthermore relates to the preparation of suchsynthetic resin dispersions and the use of films thereof as contactadhesives for self-adhesive articles.

Aqueous synthetic resin dispersions whose films are suitable as contactadhesives are usually prepared by the method of free radical emulsionpolymerization using hydrophilic assistant systems (emulsifiers and/orprotective colloids) which, inter alia, ensure a sufficient shelf lifeof the dispersion. However, these hydrophilic assistants remain in theresulting adhesive film during film formation by the dispersions andhave an adverse effect on its water resistance. Inter alia, the adhesivefilms exhibit blooming on contact with water, which is particularlydisadvantageous in the case of self-adhesive transparent films.

DE-A 37 20 860 discloses aqueous polymer dispersions which have a longshelf life and are obtainable by subsequent dispersion of a mixture oftwo copolymers in water with the addition of ammonia and polyhydrazides,one or both of the copolymers containing a carbonyl compound ascopolymerized unit. The films of these dispersions are recommended ascontact adhesives having high water resistance. However, thedisadvantage of these contact adhesives is that they containpolyhydrazides, which frequently release hydrazine in an undesirablemanner under the action of water.

It is an object of the present invention to provide aqueous syntheticresin dispersions which have a long shelf life and whose films do nothave the stated disadvantage and in particular are suitable as contactadhesives having high water resistance.

We have found that this object is achieved by the synthetic resindispersions defined at the outset.

Particularly suitable monomers I are the monocarboxylic acids acrylicand methacrylic acid, the dicarboxylic acids maleic and itaconic acid,the anhydrides of these dicarboxylic acids and half-esters thereof withthe alcohols ethanol, isopropanol, n-butanol and glycol mono-n-butylether, among which acrylic and methacrylic acid are preferred. Theamount of the monomers I in the monomer mixture A1 is advantageouslyfrom 5 to 12% by weight. The half-esters of the dicarboxylic acids canalso be introduced into the synthetic resins A in an indirect manner byreacting associated anhydride-containing synthetic resins A in solutionin an organic solvent at elevated temperatures of from 50° to 100° C.with the corresponding alcohols. Particularly suitable monomers II aremethyl acrylate, methyl methacrylate, ethyl acrylate, isopropylacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate,isobutyl methacrylate, tert-butyl acrylate, 2-ethylhexyl acrylate and2-ethylhexyl methacrylate, n-butyl acrylate and methyl methacrylatebeing preferred. The amount of the monomers II in A1 is preferably from80 to 95% by weight. A preferably used building block III is n-dodecylacrylate. Examples from the series consisting of the vinylaromaticmonomers (monomers IV) are styrene, α-methylstyrene, vinyltoluenes,tertbutylstyrenes and halostyrenes, such as the chlorostyrenes. Themonomers IV are present in Al preferably in an amount of from 5 to 15%by weight, styrene preferably being used.

The monomers V advantageously present as copolymerized units in A1 aremercaptosilanes I where n is from 2 to 4. R¹ and R² are preferablyhydrogen or methyl, while R³ and R⁵ are advantageously methyl, ethyl,methoxy or ethoxy, and one or more of the radicals R³ to R⁵ must bemethoxy or ethoxy. Particularly preferred mercaptosilanes I for thecopolymerization are 3-mercaptopropyltrimethoxysilane,3-mercaptopropyltriethoxysilane and3-mercaptopropylmethyldimethoxysilane. The mercaptosilanes I are knownand are commercially available. The amount of monomers V preferably usedin A1 is from 0.2 to 2% by weight.

Suitable monomers VI include vinyl ethers of lower alkanols, vinylesters of lower alkanecarboxylic acids, diesters of maleic, fumaric,itaconic, citraconic or mesaconic acid with monohydric alcohols of 1 to20 carbon atoms which may contain ether and/or thioether groups,monoesters of acrylic or methacrylic acid with simple alkanediols, suchas 1,2-ethanediol, 1,3-propanediol or 1,4-butanediol, acrylamide,methacrylamide, acrylonitrile, methacrylonitrile, monoolefins of 3 to 20carbon atoms, such as propene, 1-butene, 2-butene, isobutene, pentenesor hexenes, and diolefins, such as butadiene and isoprene. However, A1preferably contains no monomers (VI).

The monomer mixture A2 advantageously contains from 75 to 98% by weightof monomers II, while the amount of the monomers IV and VI in A2 ispreferably from 2 to 25% by weight and the monomers V are advantageouslypresent in a part by weight of from 0.2 to 2% by weight. The glasstransition temperatures of the homopolymers of the monomers II arestated, for example, in J. Brandrup and E. H. Immergut, Polymer Handbook1st Ed. J. Wiley, New York 1966 and 2nd Ed. J. Wiley, New York, 1975.Synthetic resins A which are prepared using from 25 to 45 parts byweight of A1 and from 55 to 75 parts by weight of A2 are preferred.

Preferred silanes II are 3-glycidyloxypropyltrimethoxysilane,2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane,2-(3,4-epoxy-4-methylcyclohexyl)-propylmethyldiethoxysilane,3-glycidyloxypropyldimethylethoxysilane and3-glycidyloxypropylmethyldiethoxysilane. The novel dispersionspreferably contain from 0.1 to 2% by weight, based on the amount of thesynthetic resin A used, of the silanes II.

For the preparation of synthetic resins A, the monomer mixtures A1 andA2 may be polymerized spatially separately in solution and then mixedwith one another, or polymerized spatially at the same point but insuccession. Synthetic resins A which are obtainable by solutionpolymerization of the monomer mixtures A1 and A2 carried out insuccession but spatially at the same point are preferred, the additionof the second monomer mixture being effected when the first monomermixture used has polymerized to a conversion of 95%, preferably 99%. Itis not important whether A1 is polymerized first and then A2 or whetherthe reverse procedure is adopted. In other respects, the process of freeradical solution polymerization for the preparation of the syntheticresins A is carried out in a conventional manner. Preferred syntheticresins A are those which have a K value of from 20 to 50, preferablyfrom 30 to 40, in acetone. The K value is a relative viscosity numberwhich is determined similarly to DIN 53,726, at 25° C. The flow rate ofa 3% strength by weight solution of the synthetic resin A in acetone ismeasured relative to the flow rate of pure acetone. It characterizes themean degree of polymerization of the polymer, which can be influenced ina known manner by controlling the polymerization conditions.Advantageously, the solution polymerization is carried out in thepresence of from 0.3 to 5.0, preferably from 0.5 to 3.0, % by weight,based on the sum of the monomers, of free radical initiators, such asazobiscarboxamides, azobiscarbonitriles or peroxides, such as tertbutylperoctoate. The polymerization temperature is as a rule from 50 to 150°C., preferably from 80 to 130° C. Polymerization is carried out in thepresence or absence of regulators, such as mercaptoethanol, tert-dodecylmercaptan or diisopropylxanthogen disulfide, which may usually bepresent in amounts of from 0 to 3% by weight, based on the sum of themonomers.

The amount of solvent used is usually from 20 to 35% by weight, based onthe total amount of monomers. Preferably used solvents are those which,owing to their boiling point and/or azeotrope formation with water, canbe readily distilled off from the novel dispersions. n-Butanol,isobutanol, propanols, ethanol and toluene are particularly preferred.

For the preparation of the novel synthetic resin dispersions, theresulting organic solutions of the synthetic resins A are usuallyadvantageously converted into a dispersion at elevated temperatures(from 60° to 80° C., preferably 70° C.), by stirring in a concentrated,preferably 25% strength by weight aqueous ammonia solution and thenstirring in pure water, and the organic solvent is removed from thesedispersions, for example by distillation, to a content of 5% by weightor less, the amount of water removed simultaneously being recycled ifrequired.

In an alternative method of preparation, a similar procedure is followedexcept that the removal of the organic solvent is carried out before theaddition of ammonia.

The amount of ammonia added is such that the pH of the novel dispersionsis from 6 to 10, preferably from 7 to 9. Some of the ammonia used forneutralization, ie. from 0 to 25 mol %, can be replaced by organicamines, in particular triethylamine. Preferably, however, only ammoniais used. The silanes II are preferably stirred in after the addition ofammonia and removal of the excess organic solvent. The solids content ofthe novel dispersions is chosen so that a viscosity favorable forprocessing results, this being advantageous in use and being effected byremoval or addition of water. Said solids content is from 35 to 60,preferably from 40 to 55, % by weight. In addition, the viscosity can bemodified by the addition of thickeners. Other possible additives areresins or plasticizers, in order to vary the adhesive properties. Thenovel synthetic resin dispersions generally have a long shelf life, ie.as a rule they do not form two phases or show altered viscosity,film-formation or adhesive behavior on prolonged storage. Their filmshave an advantageous cohesive and adhesive behavior and are suitable ascontact adhesives having high water resistance for self-adhesivearticles, for example for the production of self-adhesive tapes andself-adhesive films, in particular of protective films and decorativefilms. Suitable substrates include paper, plastics films or textiles.The substrate materials can be coated using conventional applicationunits, for example with the aid of a knife-over-roll coater. The applieddisperse layer is generally converted into a film by heating.

EXAMPLES EXAMPLES 1 TO 5

Preparation of various novel synthetic resin dispersions

General method: A solution of 60 g of a monomer mixture A1 in 60 g ofisobutanol was heated to the polymerization temperature of 105° C., and8 g of a solution L of tert-butyl peroctoate in isobutanol were addedall at once. Thereafter, a further 25 g of the solution L and theremaining amount of A1 were added continuously via separate feeds in thecourse of 1.5 hours while maintaining the polymerization temperature,and, after the feed had ended, polymerization was continued for afurther hour. A further 80 g of the solution L and a monomer mixture A2were then added to the reaction mixture at constant polymerizationtemperature via separate feeds in the course of 3 hours. Thereafter, theremaining amount of the solution L was added continuously in the courseof 2 hours, and polymerization was continued for 1.5 hours. 23.6 g of a25% strength by weight aqueous ammonia solution and 1,000 g of waterwere stirred into the resulting solution of the polymer in isobutanol at70° C. The solvent used was then separated off by distillation underreduced pressure to a content of less than 1% by weight, the amount ofwater simultaneously removed being added again. To prepare the noveldispersion, 3-glycidyloxopropyltrimethoxysilane was then stirred in asthe silane II. The dispersions thus obtained have the properties shownin Table 1. Table 1 also contains the quantitative data relating to thestarting materials used for their preparation.

                                      TABLE 1                                     __________________________________________________________________________                 Example                                                                              Example                                                                              Example                                                                              Example                                                                              Example                                           1      2      3      4      5                                    __________________________________________________________________________    A1:                                                                           Methyl methacrylate [g]                                                                    48 (16)                                                                              48 (16)                                                                              48 (16)                                                                              48 (16)                                                                              24 (8)                               n-Butyl acrylate [g]                                                                       227                                                                              (75.7)                                                                            227                                                                              (75.7)                                                                            227                                                                              (75.7)                                                                            227                                                                              (75.7)                                                                            251                                                                              (83.7)                            Acrylic acid [g]                                                                           25 (8.3)                                                                             25 (8.3)                                                                             25 (8.3)                                                                             25 (8.3)                                                                             25 (8.3)                              The () contain the amounts converted to % by weight, based on A1.        

    A2:                                                                           Methyl methacrylate [g]                                                                    112                                                                              (16)                                                                              112                                                                              (16)                                                                              112                                                                              (16)                                                                              109.5                                                                            (15.6)                                                                            56 (8)                               n-Butyl acrylate [g]                                                                       583                                                                              (83.3)                                                                            583                                                                              (83.3)                                                                            583                                                                              (83.3)                                                                            583                                                                              (83.3)                                                                            639                                                                              (91.3)                            3-Mercaptopropyltri-                                                                       5  (0.7)                                                                             5  (0.7)                                                                             5  (0.7)                                                                             7.5                                                                              (1.1)                                                                             5  (0.7)                             methoxysilane [g]                                                              The () contain the amounts converted to % by weight, based on A2.            L:                                                                            tert-Butyl peroctoate [g]                                                                  8      8      8      8      7                                    Isobutanol [g]                                                                             192    192    192    192    192                                  Silane II:   0.1    0.3    0.5    1      0.5                                  3-Glycidyloxypropyltri-                                                       methoxysilane [% by                                                           weight based on synthetic                                                     resin A]                                                                      Dispersion:                                                                   Solids content [% by wt.]                                                                  50.3   50.3   50.3   48.3   43.4                                 Isobutanol content                                                                         0.53   0.53   0.53   0.45   0.71                                 [% by weight]                                                                 pH           7.8    7.8    7.8    8.0    8.2                                  __________________________________________________________________________

EXAMPLE 6

Testing the contact adhesive properties of films of synthetic resindispersions from Examples 1 to 5

(a) Production of test strips

To produce test strips, the dispersions were applied to a polyester filmas the substrate in an amount such that the thickness of the dry layercorresponded to 25 g/m², and drying was carried out for 3 minutes at 90°C. in a drying oven. Strips 2 cm wide and 5 cm long were cut out fromthe resulting self-adhesive film.

(b) Testing the cohesion (shear strength)

To test the internal strength of the adhesive film of a noveldispersion, the test strips (a) were rolled over a length of 2.5 cm,using a weight of 2.5 kg, onto a chromium-plated steel sheet (V2A) andstored for 24 hours under standard conditions. The end of the steelsheet which was not adhesively bonded was then fastened between 2clamping jaws, and the opposite projecting self-adhesive tape, freelysuspended, was loaded with a weight of 1 kg at 25° and 50° C. The timetaken to break the adhesive film is a measure of the internal strengthof the adhesive film.

(c) Initial adhesion (immediate peel strength or initial adhesion)

To determine the initial adhesion of the test strips (a) to the surfaceof a substrate, said strips were rolled over a length of 2.5 cm, using aweight of 2.5 kg, onto a chromium-plated steel sheet (V2A). Immediatelyafterward, the force required to peel off the test strips backward in atensile strength testing apparatus at a peel angle of 180° C. and at arate of 300 mm/min without breaking the adhesive film was determined.

(d) Water resistance

To determine the water resistance, the novel dispersions were applied toa transparent polyester film in a thickness such that a 20 μm thick drylayer was obtained, and drying was carried out for 3 minutes at 90° C.in a drying oven. Thereafter, the film was clamped in a frame and, inorder to determine the light transmittance, was immersed in thewater-filled cell of a photometer at 20° C. Immediately after immersion,the light transmittance was calibrated at 100% and the decrease in lighttransmittance as a function of time was then recorded. The films of thenovel dispersions showed a decease of from 2 to 10% after 30 min, whilethe films of dispersions containing hydrophilic assistant systems show adecrease of not less than 25% in the same period.

The test values of tests (b) to (d) are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                     Dispersion from Example                                                       1    2      3      4       5                                     ______________________________________                                        Cohesion (hours), 25° C.                                                              19.5   74     64.5 >120    3.13                                Cohesion (hours), 50° C.                                                              1.9    6.0    4.9  10.0    0.4                                 Immediate peel 8.0    6.2    5.7  3.8     1.7                                 strength (N)                                                                  Light transmittance                                                                          96     97     98   91      95                                  after 30 min (%)                                                              ______________________________________                                    

We claim:
 1. An aqueous synthetic resin dispersion consisting of:(A)from 35 to 60% by weight of a synthetic resin obtained by free radicalsolution polymerization of a monomer mixture A1 and a monomer mixture A2in an organic solvent separately polymerized and then combined or insuccession spatially at the same point in an amount from 15 to 70 partsby weight of mixture A1 and from 30 to 85 parts by weight of mixture A2,wherein mixture A1 is: (a) from 1.5 to 15% by weight of at least onemonomer selected from the group consisting of α,β-monoethylenicallyunsaturated monocarboxylic acids of 3 to 5 carbon atoms,monoethylenically unsaturated dicarboxylic acids selected from the groupconsisting of maleic and itaconic acids, anhydrides and half-esters ofthese dicarboxylic acids with alkanols of 1 to 8 carbon atoms or withglycol monoethers (monomers I), (b) from 65 to 98.5% by weight of atleast one monomer selected from the group consisting of C₁₋₁₀ alkyl(meth)acrylates (monomers II), (c) from 0 to 10% by weight of at leastone monomer selected from the group consisting of C₁₁₋₂₀ alkyl(meth)acrylates (monomers III), (d) from 0 to 20% by weight of at leastone vinyl aromatic monomer (monomers IV), (e) from 0 to 5% by weight ofat least one mercaptosilane of formula I (compound V) ##STR3## where nis from 1 to 8, R¹ and R² independently of one another are each hydrogenor C₁ -C₄ -alkyl and R³, R⁴, and R⁵ independently of one another areeach C₁ -C₆ -alkyl or C₁ -C₆ -alkoxy, with the proviso that one or moreof the radicals R³ to R⁵ is alkoxy, and (f) from 0 to 10% by weight ofat least one other copolymerizable monomer (monomers VI), and mixture A2is: (a) from 60 to 100% by weight of at least one monomer II, (b) from 0to 10% by weight of at least one monomer III, (c) from 0 to 30% byweight of at least one monomer IV and VI and (d) from 0 to 5% by weightof at least one compound V, with the proviso that more than 65% byweight of the sum total of A1 and A2 is accounted for by monomers IIwhose homopolymers have a glass transition temperature of from 0° to-70° C., and an amount of compound V which differs from 0 and compound Vis incorporated as polymerized in the copolymer; (B) from 0.05 to 5% byweight, based on said synthetic resin, of at least one silane of theformula II ##STR4## wherein R⁶ is an epoxy-carrying radical and R³ -R⁵are as defined above, (C) an amount of at least one compound selectedfrom the group consisting of ammonia and organic amine such that the pHof the aqueous dispersion ranges from 6 to 10; the remainder of thecomposition being water, with the dispersion containing from 0 to 5% oforganic solvent.
 2. The aqueous synthetic resin dispersion of claim 1,wherein said copolymerizable monomer (VI) is a member selected from thegroup consisting of lower alkyl vinyl ethers vinyl esters of loweralkane carboxylic acids, diesters of maleic, fumaric, itaconic,citraconic or mesaconic acid with monohydric alcohols of 1 to 20 carbonatoms which may contain ether and/or thioether groups, monoesters ofacrylic or methacrylic acid with alkanediols, acrylamide,methacrylamide, acrylonitrile, methacrylonitrile, monoolefins of 3 to 20carbon atoms and diolefins.
 3. A method of preparing a self adhesivearticle, comprising:providing an article with a coating of the syntheticresin dispersion of claim 1 thereby forming said self adhesive articlehaving a contact adhesive coating.